Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam writing apparatus and a multi charged particle beam writing method, and more specifically, relate, for example, to a control method of the stage used in multi-beam writing.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits becomes progressively narrower year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” patterns on a wafer and the like with electron beams.
As a known example of employing the electron beam writing technique, there is a writing apparatus using multi-beams. Since it is possible for multi-beam writing to irradiate multiple beams at a time, the writing throughput can be greatly increased in comparison with single beam writing. A writing apparatus employing the multi-beam technique, for example, forms multi-beams by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in a mask, performs blanking control for each beam, reduces each unblocked beam by an optical system, and deflects it by a deflector so as to irradiate a desired position on a target object or “sample”.
The multi-beam writing apparatus employs a method, which is currently under development, of irradiating multi-beams to a plurality of corresponding pixel regions at a time while moving a stage at a constant speed on the basis of a raster scanning system. Although the stage speed is controlled at a constant speed, it may decrease due to turning of the stage at starting or finishing writing a stripe region. On such occasion, if beam on/off control is performed with a fixed shot cycle, the dose becomes excessive due to the stage speed decrease generated at the stage turning. Regarding dose adjustment for preventing such excess of the dose, there is disclosed a method of cutting a superfluous dose by a blanking mechanism (for example, refer to Japanese Unexamined Publication No. JP 2009-532887A). However, it is difficult for this method to perform writing highly accurately and improve the throughput.
If merely the beam on/off control with a fixed shot cycle is performed, dimension errors occur due to proximity effect. Then, aiming at higher accuracy in accordance with recent requirement of miniaturization, proximity effect correction by dose correction needs to be performed. In order to perform proximity effect correction by using a dose, it is necessary to variably control the dose. In addition, in the case of correcting proximity effect by using a dose, it is necessary to increase the dose in the region where the pattern density is low. Therefore, the irradiation time needs to be set long in the region with low pattern density, and to be set short in the region with high pattern density.
On the other hand, when the stage speed is controlled at a constant speed similarly to the conventional raster scanning system, the speed is determined according to the beam whose irradiation time is longest. Therefore, the stage speed is determined according to the region where the irradiation time is long and the pattern density is low. However, in the region where the pattern density is low, writing takes time because the irradiation time is long from the first, and further, if there is a region with no pattern while the stage is moving, latency exists in which merely waiting is performed without irradiating beams. Therefore, in the region with low pattern density, there may occur an inversion phenomenon in that the throughput is lower than that of the single beam writing method of a vector system. With respect to the multi-beam writing apparatus, high throughput performance in the region with high pattern density cancels out the throughput decrease caused by the inversion phenomenon, and increases the total throughput higher than that of the single beam writing method.
However, since the stage speed is determined according to the region where irradiation time is long and pattern density is low, latency to wait for a next shot occurs, even when beam irradiation has been completed, in the region where pattern density is high. Thus, inherent high throughput performance of the multi-beam writing method has not been fully achieved.